Vectorial network analyzers (VNAs) serve for the precise measurement of electronic devices and components and also active and passive radiofrequency circuits and assemblies through to antennas.
The so-called scattering parameters of n-ports (n=1, 2, . . . ) are detected, which, if appropriate, are converted into 2n-pol-parameters (e.g., Z or Y parameters).
A so-called system error correction provides for the actual possibility of carrying out precise measurements using VNAs. In modem apparatuses, the measurement accuracy of VNAs is influenced almost exclusively by the possibility of realizing the calibration standards required for the system error correction.
As it is known, the reflection and/or transmission behavior of calibration standards, which are partly or completely known objects, is measured during the system error correction in the so-called calibration operation, at several measurement locations which are to optimize in position and amount.
From these measured values, correction data (so-called error variables or coefficients) are obtained by means of special computation methods. With this correction data and a corresponding correction calculation, measured values from which system errors of the VNA and of the leads (instances of coupling=crosstalk, mismatches=reflections) have been eliminated are obtained for any desired measurement object.
The customary form of description of the electrical behavior of components and circuits in radiofrequency technology is effected by means of the scattering parameters (also called S parameters). They link wave variables with one another, rather than currents and voltages. This representation is particularly adapted to the physical conditions.
The following relationship applies to, for instance, waves a1 and a2 running up to a two-port and the waves b1 and b2, which are respectively continuing in the opposite direction:
            (                                                  b              1                                                                          b              2                                          )        =                            (                                                                      S                  11                                                                              S                  12                                                                                                      S                  21                                                                              S                  22                                                              )                          ︸                      =                                                  ⁢                          (              S              )                                          ⁢              (                                                            a                1                                                                                        a                2                                                    )              ,wherein [S] is the scattering matrix identifying the two-port.
One known calibration method for a two-port model with 10 or 12 error variables is the so-called 10-tern or 12-term method. It is also referred to as SOLT (S: Short, O: Open, L: Load=Match, T: Thru) in the American literature and as TMSO in Europe. It is the only system calibration method for two-port network analyzers with just three measurement locations, wherein each measurement location is located at the common measurement channel for both ports before the switch which switches each time one of the ports for measurement, and further measurement locations, which are arranged at the measurement channel of each port. But in this arrangement of the measurement locations, the switch is integrated in the measurement of the calibration standards.
In the case of this TMSO calibration method, which is used the most often in practice, it is necessary for the two measurement ports to be connected (T=Thru). Three known one-ports, e.g. wave sink (M=Match), short circuit (S=Short) and open circuit (O=Open), then have to be contact-connected and measured at each measurement port.
The multiport measurement problem stems from the fact that all the measurement ports are coupled to one another via the measurement object. This means that it is no longer the case that a measure of the incoming wave is obtained at one measurement location, a measure of the reflective wave is obtained at the next measurement location, and a measure of the transmitted wave is finally obtained at a further measurement location, independent of the terminations of the multiport. Rather, it is additionally necessary to take into account the reflection properties of the other measurement ports in the model.